There are well-known apparatuses and methods for implementing multiple-orifice drop-on-demand ink jet print heads. In general, each ink jet of a multiple-orifice drop-on-demand ink jet array print head operates by the displacement of ink in an ink pressure chamber and the subsequent ejection of ink droplets from an associated orifice. Ink is supplied from a common ink supply manifold through an ink inlet to the ink pressure chamber. A driver mechanism is used to displace the ink in the ink pressure chamber. The driver mechanism typically includes a transducer (e.g., a piezo-ceramic material) bonded to a thin diaphragm. When a voltage is applied to the transducer, it displaces ink in the ink pressure chamber, causing the ink to flow through the inlet from the ink manifold to the ink pressure chamber and through an outlet and passageway to the orifice.
It is desirable to employ a geometry that permits the multiple orifices to be positioned in a densely packed array. Suitably arranging the manifolds, inlets, pressure chambers, and the fluidic couplings of the chambers to associated orifices is not a straightforward task, especially when compact ink jet array print heads are sought. Incorrect design choices, even in minor features, can cause nonuniform jetting performance.
Uniform jetting performance is generally accomplished by making the various features of each ink jet array channel substantially identical. Uniform jetting also depends on each channel being free of air, contaminants, and internally generated gas bubbles that can form in the print head and interfere with jetting performance. Therefore, the various features of the multiple-orifice print head must also be designed for effective purging.
For example, U.S. Pat. No. 4,730,197 issued Mar. 8, 1988 for IMPULSE INK JET SYSTEM describes an ink jet array print head having two parallel rows of generally rectangular ink pressure chambers positioned with their centers aligned. Each one of a linear array of ink jet orifices is coupled to an associated ink pressure chamber. The central axis of each orifice extends normal to the plane containing the ink pressure chambers and intersects an extension portion of the ink pressure chamber. An ink manifold of substantially uniform cross-sectional area supplies ink to each of the chambers through a restrictive opening that acts to minimize acoustic cross-talk between adjacent channels of the multiple orifice array. However, such restrictions often trap bubbles and, as a consequence, require frequent purging. Also described is the effect of pressure chamber resonances on jetting uniformity and the use of dummy channels and compliant wall structures to reduce reflected wave-induced cross-talk in a 36-orifice ink jet print head.
Effective purging depends on a relatively rapid ink flow rate through the various features of an ink jet print head to sweep away bubbles and contaminants. Ink flow rate at various locations in an ink manifold depends on the number of downstream orifice channels being purged and the cross-sectional area of the manifold. The flow rate is, therefore, greater at the upstream end of the manifold than at the downstream end where only a single orifice channel is drawing ink. Consequently, the ink flow rate at the downstream end of the manifold may not be sufficient to sweep away entrapped bubbles and contaminants.
Some ink flow rate and nonuniformity problems are addressed in U.S. Pat. No. 4,367,480 issued Jan. 4, 1983 for HEAD DEVICE FOR INK JET PRINTER, which describes a multiple-orifice ink jet print head having uniform feature sizes in each orifice channel and an ink manifold having a nonuniform cross-sectional area that provides increased flow rate at its downstream end. However, the manifold is shaped such that flow stagnation regions can still entrap bubbles or contaminants. The print head further includes a serpentine ink inlet configuration that provides uniform acoustic performance among orifice channels and an ink supply manifold having ink inlets at both ends. Such a configuration provides for rapid ink flow rate in one ink inlet, through the manifold, and out the other inlet (cross-flow purging) that effectively removes contaminants or bubbles from the ink manifold but not from the various features of each orifice channel.
Printing speed and jetting uniformity are addressed in U.S. Pat. No. 5,087,930 issued Feb. 11, 1992 for DROP-ON-DEMAND INK JET PRINT HEAD, assigned to the assignee of this application, which describes a compact 96-orifice ink jet print head having acoustically uniform internal features. The print head is constructed of laminated plates that together form associated arrays of ink manifolds, diaphragms, ink pressure chambers, ink inlets, offset channels, and orifices. Particular plates also form black, yellow, magenta, and cyan ink manifolds that are distributed elevationally above and below the other internal ink jet features. In particular, the elevationally lower manifolds are connected to the upper manifolds by ink communication channels. Unfortunately, during periods of no printing, buoyant bubbles can become entrapped in an upper arch of the ink communication channel, and when printing, the rate of ink flow is insufficient to sweep the bubbles away through any of the ink supply channels of the print head. During purging, ink is caused to flow at an increased rate through the manifolds and ink supply channels, causing the bubbles to be drawn toward the downstream end of the upper manifold where they are unfortunately entrapped in a stagnation region.
Entrapped bubbles are a particularly serious problem because each bubble has a resonant frequency that acts to increase cross-talk among ink jet channels whenever an ink orifice channel ejects ink drops at a rate near the resonant frequency of the bubble. Moreover, at some ink drop ejection rates, sufficient energy is transferred to the bubble to cause it to grow and ultimately prevent the associated ink jet from operating.
Some solutions to bubble entrapment are addressed in co-pending U.S. patent application Ser. No. 08/056,346 filed Apr. 30, 1993 for A MULTIPLE-ORIFICE DROP-ON-DEMAND INK JET PRINT HEAD HAVING IMPROVED PURGING AND JETTING PERFORMANCE, which is assigned to the assignee of this application. A 124-orifice ink jet print head is described in which the manifolds are tapered to eliminate ink flow stagnation regions. Further, the manifolds and ink supply channels are all tilted elevationally upward and include inlet channel ports distributed along the upper edges of the manifolds such that the buoyancy of bubbles causes them to float upward in the manifolds and be easily swept into an ink supply channel. Moreover, the tapering and sizing of the manifolds and other internal ink jet features minimizes cross-talk and resonance-induced jetting nonuniformities. However, even with 124 orifices, a printer employing the print head still requires two minutes to produce a color print.
A solution to the printing speed problem is addressed in U.S. Pat. No. 4,538,156 issued Aug. 27, 1985 for INK-JET PRINTER, which describes an ink jet image transfer printer that employs a print media-width print head that ejects image-forming ink drops directly onto a rapidly rotating drum. The media-width print head employs a linear array of ink jet orifices that are spaced apart by 0.254 millimeter (0.1 inch) to print a 79 dots per centimeter (200 dots per inch) resolution image on the drum during 20 successive rotations thereof during which time the print head is laterally moved. After the drum receives the image, a print medium is placed in rolling contact with the drum to transfer the image from the drum to the print medium. Such transfer printing is advantageous because of relatively high-speed printing, insensitivity to print media thickness, and a simplified "straight through" paper path. However, the above-described printer cannot produce color prints nor can the print head orifice spacing support a printing resolution of 118 dots per centimeter (300 dots per inch) or greater.
Despite the numerous prior multiple-orifice ink jet print head designs, a need still exists for a manufacturable, purgable, ink jet print head that can produce multiple high-resolution, high-quality color prints per minute.